I. Rodríguez-Vargas

Energy states in GaAs delta-doped field effect transistors under hydrostatic pressure

The study of the electronic structure in GaAs-based delta-doped field effect transistors under applied hydrostatic pressure is presented. A combination of the depletion approximation and the local density Thomas-Fermi theory is used to model the potential energy profile. We present a discussion on the possible effect of the hydrostatic pressure in the formation of high conductivity channels in the system.

Influence of the hydrostatic pressure onto the electronic and transport properties of n-type double δ-doped GaAs quantum wells

We present a Thomas-Fermi-based envelope function calculation of the electronic structure for n-type double δd-doped GaAs quantum wells under the influence of applied hydrostatic pressure. An empirical formula for the electron mobility is used to qualitatively describe some transport properties in the system. The optimal interwell distance and hydrostatic pressure for which the mobility would be a maximum are obtained, particularly in the high density limit (above 1013cm-2). This could be of interest for the design and fabrication of high power, high speed electronics.

Self-similar transmission properties of aperiodic Cantor potentials in gapped graphene

AbstractWe investigate the transmission properties of quasiperiodic or aperiodic structures based on graphene arranged according to the Cantor sequence. In particular, we have found self-similar behaviour in the transmission spectra, and most importantly, we have calculated the scalability of the spectra. To do this, we implement and propose scaling rules for each one of the fundamental parameters: generation number, height of the barriers and length of the system. With this in mind we have been able to reproduce the reference transmission spectrum, applying the appropriate scaling rule, by means of the scaled transmission spectrum. These scaling rules are valid for both normal and oblique incidence, and as far as we can see the basic ingredients to obtain self-similar characteristics are: relativistic Dirac electrons, a self-similar structure and the non-conservation of the pseudo-spin.

Self-similar conductance patterns in graphene Cantor-like structures

Graphene has proven to be an ideal system for exotic transport phenomena. In this work, we report another exotic characteristic of the electron transport in graphene. Namely, we show that the linear-regime conductance can present self-similar patterns with well-defined scaling rules, once the graphene sheet is subjected to Cantor-like nanostructuring. As far as we know the mentioned system is one of the few in which a self-similar structure produces self-similar patterns on a physical property. These patterns are analysed quantitatively, by obtaining the scaling rules that underlie them. It is worth noting that the transport properties are an average of the dispersion channels, which makes the existence of scale factors quite surprising. In addition, that self-similarity be manifested in the conductance opens an excellent opportunity to test this fundamental property experimentally.

Angle-dependent bandgap engineering in gated graphene superlattices

Graphene Superlattices (GSs) have attracted a lot of attention due to its peculiar properties as well as its possible technological implications. Among these characteristics we can mention: the extra Dirac points in the dispersion relation and the highly anisotropic propagation of the charge carriers. However, despite the intense research that is carried out in GSs, so far there is no report about the angular dependence of the Transmission Gap (TG) in GSs. Here, we report the dependence of TG as a function of the angle of the incident Dirac electrons in a rather simple Electrostatic GS (EGS). Our results show that the angular dependence of the TG is intricate, since for moderated angles the dependence is parabolic, while for large angles an exponential dependence is registered. We also find that the TG can be modulated from meV to eV, by changing the structural parameters of the GS. These characteristics open the possibility for an angle-dependent bandgap engineering in graphene.

Hole states in diamond p-delta-doped field effect transistors

The p-delta-doping in diamond allows to create high density two-dimensional hole gases. This technique has already been applied in the design and fabrication of diamond-based field effect transistors. Consequently, the knowledge of the electronic structure is of significant importance to understand the transport properties of diamond p-delta-doped systems. In this work the hole subbands of diamond p-type delta-doped quantum wells are studied within the framework of a local-density Thomas-Fermi-based approach for the band bending profile. The calculation incorporates an independent three-hole-band scheme and considers the effects of the contact potential, the delta-channel to contact distance, and the ionized impurity density.

Fano resonances in bilayer graphene superlattices

In this work, we address the ubiquitous phenomenon of Fano resonances in bilayer graphene. We consider that this phenomenon is as exotic as other phenomena in graphene because it can arise without an external extended states source or elaborate nano designs. However, there are not theoretical and/or experimental studies that report the impact of Fano resonances on the transport properties. Here, we carry out a systematic assessment of the contribution of the Fano resonances on the transport properties of bilayer graphene superlattices. Specifically, we find that by changing the number of periods, adjusting the barriers height as well as modifying the barriers and wells width it is possible to identify the contribution of Fano resonances on the conductance. Particularly, the coupling of Fano resonances with the intrinsic minibands of the superlattice gives rise to specific and identifiable changes in the conductance. Moreover, by reducing the angular range for the computation of the transport properties it is possible to obtain conductance curves with line-shapes quite similar to the Fano profile and the coupling profile between Fano resonance and miniband states. In fact, these conductance features could serve as unequivocal characteristic of the existence of Fano resonances in bilayer graphene.

Análisis autosimilar de pozos cuánticos cuasirregulares delta dopados tipo n en GaAs

Se estudia la esctructura electronica de pozos cuanticos delta dopados tipo n en GaAs, en el cual el sistema de multiples pozos es construido de acuerdo a la secuencia de Fibonacci. Los bloques A y B corresponden a pozos delta dopados con una densidad de impurezas n2DA y n2DB, y el mismo ancho de los pozos. La aproximacion de Thomas-Fermi, el modesemi-empirico de enlace fuerte (tight-binding) sp3s* incluyendo el espin, el modelo de empalme de la funcion de Green y la matriz de transferencia fueron implementados para obtener el potencial de confinamiento, la estructura electronica y la autosimilaridad del espectro. La fragmentacion del espectro electronico se presenta cada vez que los bloques A y B interaccionan, y aumenta a medida que la diferencia de impurezas entre A y B aumenta. La funcion de onda del primer estado de las bandas fragmentadas presenta caracteristicas criticas, esto es, no es un estado localizado ni extendido, presenta caracteristicas de autosimilaridad. Por lo tanto, las caracteristicas cuasiregulares se conservan independientemente de la complejidad del sistema y pueden afectar el funcionamiento de los dispositivos basados a estas estructuras